Progress and development prospects of polycarboxylate superplasticizer polyether macromonomer
With the development of concrete technology, the requirements for polycarboxylate superplasticizers are more refined, not limited to the basic performance advantages such as water reduction rate and moisture retention. Since the polymerization of polycarboxylate superplasticizer is designable, polycarboxylate water reducing agent with special functions can be prepared according to specific engineering requirements, such as slow release type, early strength type, anti-shrinkage type and low bleed type. , low viscosity type, etc. The main steric hindrance group of the polycarboxylate superplasticizer is the longer polyoxyethylene side chain. The nature of the water-soluble nonionic polyoxyethylene soft segment allows its conformation in aqueous solution to vary. The conformational state of the side chain has a great influence on the water reducing agent. If the side chain density of the water reducing agent prepared after polymerization is small, the polyoxyethylene side chain may be biased to a freely tortuous state; if the side chain density is large, the polyoxyethylene chain may be more biased. The preparation of the polyoxyethylene side chain into a hyperbranched structure can make it have greater steric hindrance, but at the same time increase the copolymerization resistance and reduce the adsorption speed of the water reducing agent molecule, so the molecular polymerization design It is necessary to reasonably control the length of the main chain and the density of the side chains.
Excessive slump loss in concrete has always been an urgent problem for ready-mixed concrete companies, especially in high-temperature climates. The slow release type water reducing agent has the characteristics of continuous and slow release of the cement particles in a period of time, that is, the concrete with the slow release type water reducing agent has a small slump in the initial stage of stirring, but with the extension of time The slump will increase. This feature of the slow-release type water reducing agent can not only maintain the slump of the ready-mixed concrete after long-term transportation, but also avoid the concrete slump loss caused by the evaporation of the mixing water caused by long-time transportation under high temperature, and Keep the concrete slump unchanged for a certain period of time.
In the initial stage of the development of polycarboxylate superplasticizers in China, the main functional monomers are mainly MPEG and esterified unsaturated carboxylic acid-(M)AA-MPEG ester macromonomers. Due to the complicated equipment, long production cycle, high energy consumption and high cost of the ester macromonic water reducing agent in the production of polycarboxylate superplasticizer, the production process of polycarboxylate superplasticizer was gradually developed. The ether macromonomers, along with the development and variety of propylene-based polyoxyethylene macromonomers (APEG, HPEG), the polycarboxylate production process is gradually simplified, only APEG and other comonomers are lower The temperature of the polymer (40 ° C ~ 80 ° C), atmospheric pressure aqueous solution polymerization can prepare high performance polycarboxylate superplasticizer. In recent years, as the pre-isoenol start (IPEG) and the isobutylene start (HPEG) polyoxyethylene macromonomer have been successively introduced, by virtue of its higher reactivity, the obtained polycarboxylic acid product is compared with APEG. It has a greater advantage in water reduction rate and moisture retention performance. Therefore, the high performance of polycarboxylic acid with polyisoethylene macromonomer starting from (pregmental alcohol start (TPEG) and isobutylene start (HPEG) as the main raw material is reduced. Aqueous products have gradually become the mainstream products in the market of polycarboxylate water reducers. In recent years, various propylene-based polyoxyethylene ether macromonomers have been used in an amount of more than 70% of the total amount of the carboxylic acid-based polyether. Polyether production enterprises have mainly studied two aspects in the performance optimization of macromonomers. On the one hand, they are constantly looking for new initiator monomers that affect the polymerization activity of macromonomers. On the other hand, they increase or adjust by introducing new functional groups. The performance of polyoxyethylene chains.